Acoustic coupling in telephone device handsets is common and occurs when signals broadcast by the speaker of a telephone device handset are coupled to the microphone of the same telephone device handset. This acoustic coupling results in echo signals being applied to the network over which the communication channel is established. The acoustic suppression of signals broadcast by the handset speaker before they are picked up by the handset microphone is variable and depends on a number of factors, such as the pressure exerted on the user's ear by the handset speaker and how well the handset speaker seals the ear. The loss in power of these signals as a result of acoustic suppression can vary from about −50 db to as low as −24 db when the telephone device handset is placed on a hard surface. If the delay in the network is short, such as for example 30 ms, the normal acoustic suppression of signals broadcast by the handset speaker is generally sufficient to inhibit voice quality from being noticeably degraded by the echo signals picked up by the handset microphone. However, if the delay in the network is significant, echo signals applied to the network due to acoustic coupling will noticeably degrade voice quality over the communication channel. As such, suppressing echo signals resulting from acoustic coupling in telephone device handsets is important.
Echo cancelers in telephone device handsets have been considered. A typical echo canceler attempts to model the transfer function of the echo signal path using a linear algorithm such as a Least-Mean-Squared (LMS) algorithm. The estimated echo signals generated by the echo canceler are subtracted from the echo signals picked up by the handset microphone. Differences between the estimated echo signals and the actual echo signals result in error signals, which are fed back to the echo canceler. Unfortunately, since the algorithm executed by the echo canceler is linear, the echo canceler cannot deal with non-linear effects and can only converge to a transfer function which approximates the echo signals. As a result, residual echo error signals are applied to the network.
It is therefore an object of the present invention to provide a novel echo suppressor and method for suppressing echoes in a communication path.